Was Moses a missionary?
Not in the common sense of the term. In the common sense of the
term, a missionary is one who goes out from the church (within the
Christian context) to do God's work (evangelism, churchplanting,
discipleship and other forms of Christian ministry) to those
outside the church (often, but not always, cross-culturally).
Since Moses was not a Christian (since Moses lived many
centuries before Jesus Christ) and wasn't really seeking to share
his faith to those outside of his faith, he would not be thought of
as a missionary.
Of course the term missionary (etymologically) means one who is
carrying out the mission of God. Since Moses was carrying out God's
mission of bringing God's word to the Israelites, one could argue
that he was a pre-Christian model of a missionary.